Spinal fixation devices and methods of use

ABSTRACT

Placement apparatus and methods of use for impanation of spacers within an inter-vertebral disc space. In one embodiment, the load-bearing superstructure of the implant is subdivided and the bone forming material is positioned within an internal space of the placement instrument but external to the load bearing elements themselves. At least a portion of the bone graft material is freely contained within the disc space. A method of using the device is also described. In one embodiment, the placement device is used to place the implantable spacers at opposing ends of the disc space using a directly lateral surgical approach.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional patent applicationSer. No. 61/626,340 entitled “DEVICES AND METHODS FOR INTER-VERTEBRALORTHOPEDIC DEVICE PLACEMENT” by Samy Abdou and filed Sep. 23, 2011,which is incorporated herein by reference in its entirety.

COPYRIGHT

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent files or records, but otherwise reserves all copyrightrights whatsoever.

BACKGROUND 1. Field of the Disclosure

The present disclosure relates generally to the field of to bonefixation systems, components thereof, and methods of implant placementused to adjust, align and maintain the spatial relationship(s) ofadjacent bones or bony fragments after surgical reconstruction ofskeletal segments. More particularly, the present disclosure is relatedin one exemplary aspect to devices that fixate the spinous processes atone vertebral level with the spinous process of another vertebra.

2. Description of Related Technology

Whether from degenerative disease, traumatic disruption, infection orneoplastic invasion, alteration in the anatomical relationships betweenthe spinal vertebras can cause significant pain, deformity anddisability. Spinal disease is a major health problem in theindustrialized world and the surgical treatment of spinal pathology isan evolving discipline. The traditional surgical treatment of abnormalvertebral motion is the complete immobilization and bony fusion of theinvolved spinal segment and an extensive array of surgical techniquesand implantable devices have been formulated to accomplish the treatmentobjective.

Vertebral fusion may be accomplished by using an anterior, lateral orposterior approach and each has particular advantages and draw backs.Frequently, circumferential fusion of the unstable level with fixationof both the anterior and posterior aspect of the spine is desired. Thisrequires that patients undergo a combination of the aforementionedapproaches. The anterior or lateral approaches are used to insert thebone graft and load bearing implants into the disc space between theadjacent vertebras while the posterior approach is used to place bonescrews or similar fasteners that are used to immobilize the vertebralbodies.

Current implants to fuse the intervertebral disc space are usuallycomprised of an external superstructure that is capable of bearing theload transmitted across the implanted intervertebral disc space. Aninternal cavity is used to house and contain bone graft or bone graftsubstitute (collectively referred to as bone graft material) wherein thebone graft material is in contact with a bony surface of each of thevertebral bones that border the implanted disc space (i.e., thevertebral bones above and below the implant disc space). These devicesare known in the art, see e.g. U.S. Pat. Nos. RE37,479; 4,820,305;5,609,637; 5,749,916; 5,865,848; 5,888,224; 5,980,522; 6,071,310;6,086613; 6,159,244; 6,176,882; 6,206,922; 6,471,724; 6,582,431;6,616,695, each of the foregoing being incorporated herein by referencein its entirety.

Given the large number of operative approaches and the substantialanatomical variation between vertebral levels within the same individualor across different individuals, the intervertebral disc implants mustbe manufactured and provided to the surgeon in a large range of sizesand configurations. This mandates that a large number of different sizesmust be made and inventoried—adding to cost for manufacturer, vendor,and end user (hospitals). More importantly, the pre-manufactured devicesmay provide a suboptimal fit, since the surgeon must choose at the timeof implantation from a series of pre-manufactured sizes andconfigurations that may not fit each and every patient.

SUMMARY

Disclosed herein are, inter alia, placement instruments and methods ofuse for impanation of spacers within an inter-vertebral disc space. Inone embodiment, the load-bearing superstructure of the implant issubdivided and the bone forming material is positioned within aninternal space of the placement instrument but external to the loadbearing elements themselves. At least a portion of the bone graftmaterial is freely contained within the disc space.

The disclosed exemplary devices and methods may be adapted for use inany known surgical approach to the vertebral column. By way ofnon-limiting example, the device and method of implantation will beillustrated in a lateral approach to the anterior column of the spinalcolumn.

In another embodiment of this procedure, a lateral tissue corridor isused to position an implant at the lateral border of the vertebralcolumn. The intervertebral disc space that has been targeted forimplantation is entered at its lateral border.

The implant is in one embodiment comprised of at least one spacer thatis used to bear at least a portion of the load transmitted through thevertebral bodies and across the disc space. The spacer in one variantdoes not contain a bone graft cavity. The spacer may contain at leastone feature adapted to increase fixation to bone, such a bores for screwfixation, an affixed keel and/or rotatable bone fixation member.

In an embodiment, the bone graft material is contained within theplacement instrument that is used to deliver the implant to theimplantation site. The placement instrument positions the bone graftmaterial in a desired relationship to a spacer(s), wherein the latter isused to bear at least a portion of the vertical load transmitted acrossthe implanted disc space. (The so-called “vertical load” refers to theload that would normally be transmitted across the disc space of asubject standing erectly. It is understood that the vertical loadexperienced by an individual disc space will vary with the level of thatdisc space in the vertebral column. In general, more caudal disc spacelevels will experience higher vertical loads than more cephalad discspace levels.) The spacer(s) and bone graft material are delivered intothe disc space in the desired configuration. In another embodiment, thebone graft is positioned outside of one or more spacers that arecollectively and concurrently delivered into the disc space by theplacement instrument. In this embodiment, no additional bone graftmaterial is enclosed within an internal cavity of any of the spacers.

In yet another embodiment, the bone graft material is positioned withinthe placement instrument both on the outside of the one or more spacersand also within a internal cavity of at least one spacer. In anotherembodiment, the bone graft material is positioned within the internalcavity of one or more spacers, but no additional graft material ispositioned within the placement instrument and outside of the spacer(s).

After delivery of the implant assembly to the target disc space, theplacement instrument is uncoupled from the implant/bone graft materialand removed from the body cavity of the subject. The spacer(s) and bonegraft material are left within the target disc space. In one embodiment,the implantation procedure is performed through a percutaneous orminimally invasive surgical procedure.

A method of device use is illustrated, wherein the placement device isused to place the implantable spacers at opposing ends of the disc spaceusing a directly lateral surgical approach.

The details of one or more embodiments are set forth in the accompanyingdrawings and description below. Other features, objects, and advantageswill be apparent from the following description, the accompanyingdrawings and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects will now be described in detail with referenceto the following drawings. Generally speaking the figures are not toscale in absolute terms or comparatively but are intended to beillustrative. Also, relative placement of features and elements may bemodified for the purpose of illustrative clarity.

FIG. 1 are a schematic representations of a vertebral bone.

FIGS. 2A and 2B are a schematic representations of a Functional SpinalUnit (FSU) comprised of two adjunct vertebral bones and an interveningdisc space.

FIG. 3 illustrates the posterior aspect of a subject.

FIG. 4 is a schematic representation of a human torso in cross-section.

FIG. 5 illustrates an assembled embodiment of the present disclosure.

FIG. 6 illustrates section views of the disclosed instrument 130.

FIGS. 7 and 8 are exploded and assembled views of the placementinstrument 130 and the attached spacers/implants.

FIGS. 9 and 10 are perspective and orthogonal views of the deviceassembly.

FIGS. 11 and 11A illustrate the implantable spacers of the presentdisclosure.

FIG. 12 illustrates views of the implantable spacer 150.

FIGS. 13A, 13B, 14A, and 14B illustrate an exemplary instrument 130configured to retain implantable spacers 140 at a variable distancerelative to the spacer 150.

FIGS. 15, 16, and 17A show a Functional Spinal Unit (FSU) before andafter implantation.

FIG. 17B illustrates a top surface of a vertebral bone and theepiphyseal ring.

FIG. 18 is a cross sectional view of the implanted FSU with theinstrument 130 in place.

FIGS. 19A and 19B illustrate the implantable spacers 140 and 150 afterremoval of the instrument 130.

FIG. 20 illustrates an alternative screw trajectory in the placement ofa larger tissue dilator over the tissue dilator of FIG. 19B.

FIGS. 21A and 21B illustrate a change in vertebral alignment in thecoronal and/or sagittal planes from placement of implantable spacers ofvarying sizes.

FIGS. 22A and 22B illustrate the implantable spacers 140 and 150 afterremoval of the disclosed instrument 130.

FIGS. 23, 24 and 25 illustrate the screw locking member 190 inperspective views and after attachment to the implantable spacer 140.

FIGS. 26 and 27A illustrate the use of a curvilinear embodiment of thepresent disclosure.

FIG. 27B illustrates a cross section view of the curvilinear embodiment.

FIG. 28 illustrates an exploded view of an alternative deviceembodiment, wherein a placement instrument 230 is used.

FIG. 29 illustrates an alternative implantable spacer 240.

FIGS. 30A and 30B illustrate the assembly comprising the instrument 230and the implantable spacer 240.

FIG. 31 illustrates sectional views of the assembly of FIG. 29 .

FIGS. 32A and 32B illustrate an exemplary instrument 230 configured toretain the implantable spacers 240 at a variable distance relative tothe spacer 150; the distance between the implantable spacers can be readdirectly from the instrument 230.

FIGS. 33A, 33B, 34A, and 34B illustrate alternative embodiments of theimplantable spacer 140.

FIGS. 35 and 36 illustrate an additional embodiment of the implantablespacers.

FIGS. 37A and 37B illustrate an exemplary implantable spacer 350 in anexpanded and non-expanded configuration.

FIG. 38 illustrates a protrusion 35045 of segment 3504 and thecomplimentary bore 35025 of segment 3502.

FIGS. 39A and 39B illustrate an exemplary screw 170 which is configureto compliment the bore 3508.

FIG. 40A illustrates exemplary rotation of the expander 370 relative tothe spacer 350 to increase the length L of the implant 350.

FIG. 40B illustrates the expanded implant 350 after removal of screw 170and expander 370.

FIG. 41A illustrates an exemplary segment 380 coupled to an expandedspacer 350 and a second exemplary segment 380 positioned to be advancedinto cavity 3509.

FIG. 41B illustrates an exemplary segment 380,

FIG. 42 illustrates an exemplary procedure for using the instrument 130to attach the implantable spacer 350 prior to expansion.

DETAILED DESCRIPTION

In order to promote an understanding of the principles of thedisclosure, reference is made to the drawings and the embodimentsillustrated therein. Nevertheless, it will be understood that thedrawings are illustrative and no limitation of the scope of the claimsis thereby intended. Any such alterations and further modifications inthe illustrated embodiments, and any such further applications of theprinciples of the disclosed devices as illustrated herein arecontemplated as would normally occur to one of ordinary skill in theart.

Detailed Description of Exemplary Embodiments

FIG. 1 is a diagrammatic representation of a spinal vertebral bone 802in multiple views. For clarity of illustration, the vertebral bone ofFIG. 1 and those of other illustrations presented in this applicationare represented schematically, and those skilled in the art willappreciate that actual vertebral bodies may include anatomical detailsthat are not shown in these figures.

Further, it is understood that the vertebral bones at a given level ofthe spinal column of a human or animal subject will contain anatomicalfeatures that may not be present at other levels of the same spinalcolumn. The illustrated vertebral bones are intended to genericallyrepresent vertebral bones at any spinal level without limitation. Thus,the disclosed devices and methods may be applied at any applicablespinal level.

Vertebral bone 802 contains an anteriorly-placed vertebral body 804, acentrally placed spinal canal and 806 and posteriorly-placed lamina 808.The pedicle (810) segments of vertebral bone 802 form the lateral aspectof the spinal canal and connect the laminas 808 to the vertebral body804. The spinal canal contains neural structures such as the spinal cordand/or nerves. A midline protrusion termed the spinous process (SP)extends posteriorly from the medial aspect of laminas 808. A protrusionextends laterally from each side of the posterior aspect of thevertebral bone and is termed the transverse process (TP). A righttransverse process (RTP) extends to the right and a left transverseprocess (LTP) extends to the left. A superior protrusion extendssuperiorly above the lamina on each side of the vertebral midline and istermed the superior articulating process (SAP). An inferior protrusionextends inferiorly below the lamina on each side of the vertebralmidline and is termed the inferior articulating process (IAP). Note thatthe posterior aspect of the pedicle can be accessed at an indentation811 in the vertebral bone between the lateral aspect of the SAP and themedial aspect of the transverse process (TP). In surgery, it is commonpractice to anchor a bone fastener into the pedicle portion of avertebral bone by inserting the fastener through indentation 811 andinto the underlying pedicle.

FIGS. 2A and 2B illustrate a functional spinal unit (FSU), whichincludes two adjacent vertebrae and the intervertebral disc betweenthem. The intervertebral disc resides between the inferior surface ofthe upper vertebral body and the superior surface of the lower vertebralbody. (Note that a space is shown in FIGS. 2A and 2B whereintervertebral disc would reside.) FIG. 2A shows the posterior surfaceof the adjacent vertebrae and the articulations between them while FIG.2B shows an oblique view. Note that the FSU contains a three jointcomplex between the two vertebral bones, with the intervertebral disccomprising the anterior joint. The posterior joints include a facetjoint 814 on each side of the midline, wherein the facet joint containsthe articulation between the IAP of the superior vertebral bone and theSAP of the inferior bone.

The preceding illustrations and definitions of anatomical structures areknown to those of ordinary skill in the art. They are described in moredetail in Atlas of Human Anatomy, by Frank Netter, third edition, IconLearning Systems, Teterboro, N.J. The text is hereby incorporated byreference in its entirety.

In one aspect of the present disclosure, instruments and methods thatpermit a surgeon to position an implant assembly within anintervertebral disc space are provided. In an embodiment, the bone graftmaterial is contained within the placement instrument that is used todeliver the implant to the implantation site. The placement instrumentpositions the bone graft material in a desired relationship to aspacer(s), wherein the latter is used to bear at least a portion of thevertical load transmitted across the implanted disc space. (The verticalload refers to the load that would normally be transmitted across thedisc space of a subject standing erectly. It is understood that thevertical load experienced by an individual disc space will vary with thelevel of that disc space in the vertebral column. In general, morecaudal disc space levels will experience higher vertical loads than morecephalad disc space levels.) The spacer(s) and bone graft material aredelivered into the disc space in the desired configuration.

In one embodiment, the bone graft is positioned outside of one or morespacers that are collectively and concurrently delivered into the discspace by the placement instrument. In this embodiment, no additionalbone graft material is enclosed within an internal cavity of any of thespacers. In another embodiment, the bone graft material is positionedwithin the placement instrument both on the outside of the one or morespacers and also within a internal cavity of at least one spacer.

In yet another embodiment, the bone graft material is positioned withinthe internal cavity of one or more spacers, but no additional graftmaterial is positioned within the placement instrument and outside ofthe spacer(s).

While the device and the procedure are illustrated using a lateralprocedure to position the implant assembly into the disc space of thelumbar spine, it is understood that the device may be used to position aimplant assembly into the disc space at any level and using any approachto the spinal column.

In preparation for percutaneous placement of the implant into a spinallevel, the patient can be, but is not necessarily, placed in a prone orlateral decubitus position. The level of the spine that is to beimplanted can be localized on X-ray in at least one plane. After thecustomary sterile preparation of the operative site, the surgeon canlocalize an incision point on the skin that is substantially directlylateral to the spinal segment that will be implanted. FIG. 3 shows aschematic representation of the posterior aspect of a subject. The skinoverlying the back is shown. The midline is labeled and approximates themid-sagittal plane of the vertebral column. Lines Y show the lateralextent of the transverse processes of the spinal column. Assuming thatthe spinal level to be accessed is at line Z, the surgeon can make anincision at or about circle X.

FIG. 4 illustrates a cross sectional view of the torso (positionedprone) at the level of the lumbar spine. For clarity of illustration,the contents are represented schematically and those skilled in the artwill appreciate that an actual cross section of the human torso mayinclude anatomical details not shown in FIG. 4 . A lateral corridor 105can be made from the flank, through the psoas muscle 106 and onto thelateral aspect of the disc space at the spinal level to be implanted. Animplant can be placed through the corridor 105 and into disc space oronto the spine. The procedure is known to those skilled in the art andknown by differing names, such as the “XLIF” procedure (see “ExtremeLateral Interbody Fusion (XLIF): a novel surgical technique for anteriorlumbar interbody fusion.” By Ozgur, Aryan et al. in Spine J. 2006July-August; 6(4):435-43, which is hereby incorporated by reference inits entirety.) Variations of the operation are also known as DirectLateral Interbody Fusion (DLIF) and the like.

An instrument (not shown) is passed through corridor 105 and onto thelateral aspect of the psoas muscle 106. The instrument is advancedthrough the muscle and into the disc space. Since important nervestructures may transverse the psoas muscle, the instrument (and/or aprobe or device placed through a channel of the instrument) is connectedto an Electromyography (EMG) apparatus (or any other electrical systemthat is used to localize nerve tissue), and used, at least partially, asan EMG probe during advancement through the muscle. In this way, theadvancement of the instrument through the psoas muscle is performedunder EMG guidance. Under X-ray visualization, the instrument is placedinto the disc space. At least a portion of the disc material is removedfrom within the disc space through the established corridor. After thediscectomy is performed and the bony end plates have been decorticatedand prepared, at least one spacer and bone graft material (and/or bonegraft substitute) is placed within the evacuated portion of the discspace. With time, the graft material will form a bony bridge between thetwo vertebral bodies and fuse them. As described, the procedure isperformed in a percutaneous manner and under x-ray. A wider incision maybe employed and portions of the procedure, such as the discectomy, maybe performed under direct vision and using minimally invasive surgicaltechnique.

Instrument 130 is used to position at least one spacer into thepartially evacuated disc space. (The implantation is preferably, but notnecessarily, performed in a percutaneous manner.) The implanted spacerfunctions to bear at least a portion of the load transmitted through thedisc space. Instrument 130 also places the bone graft or bone graftsubstitute (collectively called bone graft material) into the discspace. The bone graft material is delivered in prescribed spatialrelationship to the spacer(s). In the illustrated embodiment, thespacer(s) will not contain an internal cavity configured to house a bonegraft material. However, it is understood that one or more of theimplanted spacers may alternatively comprise an internal cavityconfigured to house bone graft material, wherein the house bone graftmaterial is in communication with each of the vertebral bones thatborder the implanted disc space.

An embodiment of instrument 130 is shown in FIGS. 5 and 6 . Instrument130 has handle 1302, side members 1304 and an indentation 1305 at oneend of each side member 1304. Surface 1306 is positioned between sidemembers 1304. A bore 1308 transverses handle 1302.

FIG. 7 shows instrument 130 and two spacer implants in the disassembledstate while FIG. 8 shows the assembled device. Spacers (alternativelylabeled “implant”) 140 and 150 are attached to instrument 130 usingscrews 160 and 170, respectively. The assembly is shown in three planesin FIG. 9 . Sectional views are shown in FIG. 10 . Spacer 140 is shownin FIG. 11 while spacer 150 is illustrated in FIG. 12 . Preferably, butnot necessarily, each spacer does not have a medial to lateral dimensionthat is greater than one half of the medial to lateral dimension of theimplanted disc space. That is, each of width A of spacer 140 (FIG. 11A)and width B of spacer 150 (FIG. 12 ) is less than on half of the valueof the width W of the implanted disc space (the width of the disc spaceis the maximum disc space dimension in the coronal plane of the spine—asshown in FIG. 21B).

Implantable spacer 140 has central body 1402 that is inserted into thedisc space and maintains the distance between the adjacent bodies andthe height of the disc space. Body 1402 may be comprised of any materialthat is adapted for biological implantation, including a segment of bone(allograft or autograft that is harvested and shaped at the sameoperation) that is affixed onto a side plate member (as shown in FIG.11A). In one variant, the upper and/or lower surfaces 14022 of body 1402contain surface protrusions or textures (not shown) that increasefixation of these surfaces onto the abutting bone.

A side member 1404 is adapted to be positioned onto the side of each ofthe vertebral bodies. At least one bore 1406 is positioned within atleast one side member 1404 and permits placement of bone screw into theside of at least one vertebral body. The surface (14042) that abuts theside surface of the vertebral bone may have one or more protrusions (notshown), such as, for example, spike, that penetrate and fixate into saidbone. Spikes adapted for bone fixation are well known in the art and areshown in US 2004/0162558 and others. (The citation is herebyincorporated by reference in its entirety). A curvilinear surface 1407permits interaction of the spacer 140 with curvilinear surface 1306 ofinstrument 130. A threaded bore hole 1409 is contained within centralbody 1402 of spacer 140 and, in assembly with instrument 130, acceptsthe threaded end of screw 160.

While each of end height K and end height L of body 1402 (FIG. 11 ) isshown as being of equal length, it is contemplated that each of heightsK and L may alternatively be different. In this may, the implant may beused, for example to impart a greater height to the anterior disc spacethan the posterior disc space and impart a lordotic curvature onto theimplanted FSU segment (FIG. 21A—in sagittal view). It is furthercontemplated that spacer 140 may be alternatively comprised of asubstantially solid member (for example, a rectangular or trapezoidmember that is similar to body 1402) without any side members 1404 thatextend onto the side of vertebral bones.

Implantable spacer 150 has central body 1502 that is inserted into thedisc space and maintains the distance between the adjacent bodies andthe height of the disc space. Body 1502 may be comprised of any materialthat is adapted for biological implantation, including being at leastpartially comprised of a segment of bone (whether allograft orautograft). The upper and/or lower surfaces 15022 of body 1502 maycontain surface protrusions or textures (not shown) that increasefixation of these surfaces onto the abutting bone. At least one sidemember 1504 is adapted to interact with indentation 1305 at one end ofeach side member 1304 of instrument 130. A threaded bore hole 1508 iscontained within central body 1502 of spacer 150 and, in assembly withinstrument 130, accepts the threaded end of screw 170.

While each of end height K and end height L of body 1502 (FIG. 12 ) isshown as being of equal length, it is contemplated that each of heightsK and L may alternatively be different. In this way, the implant may beused, for example to impart a greater height to the anterior disc spacethan the posterior disc space and impart a lordotic curvature onto theimplanted FSU segment (FIG. 21A—in sagittal view). Further, the heightsof bodies 1402 and 1502 may be different so as to change the vertebralalignment in the coronal plane of the spine—such as, for example, inscoliosis. The latter is illustrated in FIG. 21B illustrates a coronalplane section of the vertebral bones that surround an implanted discspace. Note the coronal plane curvature created by the different sizedimplants 140 and 150.

FIGS. 13 and 14 illustrate how instrument 130 may be used to positionimplants 140 and 150 into the target disc space with a variable distancebetween them. FIGS. 9, 10, 13A and 14A illustrate implant 140 attachedto screw 160 and threadedly attached with surface 1407 abutting surface1306 of instrument 130. Note that the end segment 1602 of screw 160 ispositioned between the end of instrument 130 and end 1702 of screw 170.With rotation of end 1602 in a first direction, implant 140 will bedisplaced towards implant 150 by the threads of screw 160. With rotationof end 1602 in an opposite direction, implant 140 will be moved awayfrom implant 150 until surface 1407 abuts surface 1306 of instrument130. In this way, instrument 130 may be used to position implants 140and 150 into the target disc space with a variable distance betweenthem. FIGS. 13B and 14B illustrate implant 140 having been displacedtowards implant 150. Note that space A is now positioned between implant140 and surface 1306 on instrument 130.

Method of Use

Patient positioning, incision placement, the surgical corridor used, andtraversal of the psoas muscle (including under electrophysiologicalmonitoring (EMG) and the like) were described above and will not berepeated herein.

FIG. 15 shows a diagrammatic representation of two vertebral bodies andan intervening disc space in multiple views. For clarity ofillustration, the vertebral bodies are represented schematically andthose skilled in the art will appreciate that actual vertebral bodiesinclude anatomical details not shown in FIG. 15 . As mentioned, at leasta partial removal of the disc material is performed before implantationof the spacers 140 and 150 and bone graft material between them. Thearea of disc space that is evacuated of disc material may be slightlylarger than the distance between the outer surfaces of side members 1304of instrument 130. FIG. 16 illustrates the assembly of FIG. 9 (comprisedof instrument 130, spacer 140, spacer 150, screw 160 and screw 170)inserted into the disc space between two vertebral bodies using alateral approach (corridor 105, FIG. 4 ). Before insertion, a bone graftmaterial is placed within cavity 137 that is contained between sidemembers 1304, spacer 140, and spacer 150 in the assembled device. Thebone graft material is at least partially delivered into the disc spacewhile in cavity 137. In one embodiment, the bone graft material iscontained with a cavity of those members that will be left implanted inthe disc space. The graft material is contained in a cavity of theplacement instrument and the instrument, upon removal from the discspace, leaves the graft material freely positioned within the disc spaceand in between spacer 140 and 150 (see FIGS. 19A and B). That is, in oneembodiment, the bone graft material is not contained within an internalcavity of the implanted spacers themselves. FIG. 17A illustrates theinsertion in multiple orthogonal planes.

In one exemplary embodiment, the width of the disc space is firstmeasured. The width of the disc space, W (FIG. 22B), is equal to thegreatest distance from a lateral side surface to an opposing lateralside surface of the target disc space when measured in a coronal planeof the disc space. The placement instrument is the selected so that thelateral length, L (FIGS. 6 and 9 ), from surface 1306 to the end issubstantially equal to the width, W, of the disc space. In this way,when spacers 140 and 150 are affixed to the instrument 130, the totaldistance from the outside surface of spacer 140 to the outside surfaceof spacer 150 is substantially equal to the width, W, of the disc space.It is appreciated that in one embodiment the length L is at least equalto the width W. in another embodiment, the length L is slightly greaterthan the width W, in order to enable the device to allows for someaccommodation of length—as is shown in FIGS. 14B and 28 through 32 .

Note that at least a segment of each of spacers 140 and 150 may bepositioned overlying the epiphyseal ring of the vertebral bonesimmediately superior and inferior (i.e., that border) the implanted discspace. The epiphyseal ring is illustrated in FIG. 17B, wherein an viewof the superior aspect of a vertebral bone is shown (the numbers are asshown in FIG. 1 ). The epiphyseal ring forms the strongest portion ofthe superior and inferior surfaces of the vertebral body, which are thevertebral surfaces that border the intervertebral disc spaces. (Theepiphyseal ring is more fully discussed in: The epiphyseal ring: a longforgotten anatomical structure with significant physiological function.Dar G, et al. Spine. 2011 May 15; 36(11):850-6. The article is herebyincorporated by reference in its entirety).

A cross sectional view (in the coronal plane of the spine) is shown inFIG. 17B. Note that members 1406 abut the lateral aspect of thevertebral bodies. Each of spacers 140 and 150 are on opposing sides ofthe disc space. Cavity 137 is packed with bone graft material and restsbetween the two spacers 140 and 150, wherein, in one embodiment, thebone graft material is not contained within a spacer cavity. (It is alsocontemplated that, in an embodiment, at least one of spacers 140 and 150may contain a cavity for bone graft material—in addition to the bonegraft material contained between then in cavity 137.)

Bone screws 152 are placed through bore holes 1406 and into theunderlying bone. Screws 170 and 160 are unthreaded and removed.Instrument 130 is then removed, leaving the bone graft material withinthe evacuated disc space. FIGS. 19A and 19B illustrate the implantedspacer (the bone graft material resides between the spacers). In analternative screw trajectory, shown in FIG. 20 , the bone screws areaimed so that the distal aspect of at least one bone screw is aimedtowards the disc space. In an embodiment, the distal end of at least onescrew is anchored into spacer 150. (Note that bores 1406 of implantablespacer 140 permit placement of the bone screws in the trajectory of FIG.19B or 20 . That is, the same device embodiment permits variabletrajectory.)

Preferably, but not necessarily, a device member and/or feature may beadded to lock the bone screws to spacer 140. Plate-to-screw lockingfeatures are well known in the art and any applicable suchfeature/device may be used here. An illustrative example embodiment isshown in FIG. 23 . Locking plate 190 has a first surface 192 withcurvilinear central protrusion 1922 that is adapted to face (but notcontact) surface 1407 of spacer 140. A non-threaded bore hole 1924 isadapted to accept a locking screw 196. When seated, the threaded end ofscrew 196 interacts with complimentary threads of bore 1409 of spacer140. At least one additional protrusion 1927 extends from surface 192.In use, protrusion 1927 is adapted to forcefully abut the (head) portionof a bone screw 152 that reside within bore hole 1406. In this way,advancement of locking screw 196 into threaded hole 1409 provides aforce that drives protrusion 1927 into bone screw 152 and immobilizesthe bone screw relative spacer 140. The implanted locking plate 190 andlocking screw 196 are shown in FIG. 24 . A sectional view with lockingplate 190 in the deployed position is shown in FIG. 25 . Note that thelocking mechanism locks both the screw above and the screw bellow theimplanted disc space.

While use of instrument 130 and attached spacers has been illustrated ina straight lateral approach to the inter-vertebral disc space, thedevices may be used in an anterior, posterior, oblique or any otherknown approach to the disc space. Further, the device may be easilyconfigured for use in a curvilinear approach to the disc space. Anillustrative example of a curvilinear approach to the disc space isshown in FIG. 26 . In preparation for percutaneous placement of anorthopedic implant into a spinal disc space, the patient is placed inthe prone position with spine and skin 102 in the superior position. Thelevel of the spine that is to be implanted is localized on X-ray in atleast one plane. After the customary sterile preparation of theoperative site, the surgeon localizes an incision point that is lateralto the paraspinal muscles (the erector spinae muscle group 215 and/orothers, for example) but not directly lateral to the side of the discspace. At least one finger 210 may be placed into the retro-peritonealspace and the lateral aspect of the psoas muscle 216 is palpated, asshown in FIG. 26 . Alternatively, the surgeon can identify the psoasmuscle by inserting an instrument instead of using direct digitalpalpation.

A curvilinear instrument 205 is shown in FIG. 27A. Instrument 205 issimilar to instrument 130 but contains a curvilinear connection 2053between the handle 2052 and the end segment that attaches the implants(the end segment contains side members 2054). As in the prior embodimentof FIGS. 9 and 10 , member 260 affixes implant 140 to the instrument205, whereas member 270 affixes implant 150 to the instrument 205.Member 260 has a first end 2602, an opposing threaded end and is atleast partially malleable there between. Similarly member 270 has afirst end 2702, an opposing threaded end and is at least partiallymalleable there between. As shown in the section view of FIG. 27 b ,members 260 and 270 are malleably configured to be positioned within thesubstantially linear portion of handle 2302 and also within thesubstantially non-linear portions of connection 2303.

FIGS. 13 and 14 illustrated how instrument 130 can retain each ofspacers 140 and 150 at a variable distance from one another. FIGS. 28 to32 illustrate a device embodiment wherein the distance between each ofimplants 140 and 150 is displayed by the instrument. That is, thecurrent embodiment differs from the prior embodiment in that it containsan indicator of distance between implant 140 and 150. Whereas thedistance between the implants 140 and 150 of the prior was determined bymeasuring that distance with a separate measuring device (ruler,caliper, and the like), the current embodiment contains a distanceindicator.

FIG. 28 illustrates an exploded view of the current embodiment. Theexploded view is similar to that of FIG. 7 . Member 150, 170 and 160 areunchanged. Instrument 130 is replaced by instrument 230, wherein sidemembers 2304 differ from side member 1304 in that each member 2304contains a full thickness channel 23042 that extends proximally towardscurvilinear surface 1306 from end indentation 1305. (A magnification ofthe end segment on instrument 230 is also shown in FIG. 28 .) Markingsare displayed on the outer side surface of each member 2304, from whichthe distance between implant 140 and 150 may be ascertained. While themarkings are shown as “hatch marks” in the illustrations, it isunderstood that numbers, letters or any other notation may be used toindicate the distance of the marking from implant 150. The notations mayexpress distance in a known unit of measure or they may use an arbitraryscale that is disclosed to the user in the instrument's instructionmanual.

Implant 240 is illustrated in FIG. 29 . Because it's substantiallysimilar to implant 140 (FIG. 11 ), the same numbering scheme is used toillustrate it. It differs from implant 140 in having a side protrusion242 on each side of the implant. Each protrusion 242 is sized and shapedto slidably move in one of each channel 23042 of instrument 230. Amarking 2424 is found on the outer side surface of protrusion 242 andfunctions as a pointer that displays implant 242's position relative tothe markings on the side surface side member 2304 of instrument 230. Inthis way, marking 2424 can be used to directly read the distance betweenimplant 150 and 240.

The device is show in the assembled configuration in FIG. 30 and incross section in FIG. 31 . In FIG. 32 , screw 160 has been rotated (viaend 1602) and implant 240 has been moved towards implant 150 and awayfrom curvilinear surface 1306. With movement, space B is now positionedbetween implant 240 and surface 1306. Comparison of FIGS. 30B and 32Bshow the movement of marking 2424 relative to the side markings ofmember 2304.

As previously disclosed, spacer 140 need not have a side member 1404 forattachment onto the side of the vertebral bones. FIG. 33A illustratesspacer 140 without either side members 1404. In this embodiment, thetotality of the spacer 140 may be contained within the implanted discspace. FIG. 33B shows the section through the implanted vertebral bonesand disc space.

FIG. 34 illustrate a spacer 140 that is similar to that of FIG. 33 butis configured to contain bore holes 1409 within body 1402, wherein saidbores are configured to accept bone screws 199 that can anchor thespacer 140 directly into the adjacent vertebral bones. At least two boreholes 1409 are positioned within implant 140 so that at least one bonescrew 199 is anchored into each of the vertebral bones above and belowthe implanted disc space. The screws are not placed into bone in aparallel trajectory, so as to enhance the fixation strength of spacer140. The implanted spacer 140 may be contained within the disc space andmay have no additional member positioned to abut additional sidesurfaces of the vertebral bones. While not specifically illustrated,each screw may be further locked to spacer 140 after implantation. Manyscrew to plate locking mechanism are known in the art and any applicablemechanism may be employed. The implanted device is shown in FIG. 34B.

FIG. 35 illustrates an alternative embodiment of the implantable spacerimplants. An extension member 250 is attached to the top (and/or bottomor side) surface to at least one of implant 140 and 150. When attachedto the top and/or bottom surface of at least one implant, the extensioncan be positioned into a cut bone channel 255, as shown in FIG. 36 . Theextension may be wholly contained within the cut channel 255 or somesegment of said extension 250 may extend out of the vertebral bone, suchas, for example, into the disc space. The extension 250 is less thetotal width (when measured at its greatest extent) of the upper and/orlower vertebral bone. The width W is shown in FIG. 22B. While extension250 is shown attached to the upper and lower surface of the implant inFIGS. 35 and 36 , it is alternatively attached to a side surface (suchas surface 1505 of implant 150, or surface 1405 of implant 140) of saidimplants and rest at least partially within the disc space onimplantation. In this embodiment, extension 250 would at least partiallyenclose bone graft cavity 137.

An alternative embodiment of member 150 is illustrated as implantablespacer 350. In this embodiment, spacer 350 is of variable length and iscomprised of two slidable segments 3502 and 3504. The body of slidablesegment 3502 cooperatively interdigitates with the body of slidablesegment 3504. The upper and/or lower surfaces 35022 and 35042 maycontain surface protrusions or textures (not shown) that increasefixation of these surfaces onto the abutting bone. A threaded bore hole3508 (threads not shown) is contained within the body of slidablesegment 3505, wherein the bore hole receives the threaded end of screw170.

FIG. 37A illustrates implantable spacer 350 in a non-expandedconfiguration whereas FIG. 37B shows spacer 350 after expansion. (Notethat length L is greater in the expanded state than in the non-expandedstate.) FIG. 38 shows protrusion 35045 of segment 3504 and thecomplimentary bore 35025 of segment 3502. FIG. 39 illustrate screw 170,wherein the distal end is configured to have threads complimentary tothose of bore 3508 (threads not shown). In addition, cam expander 370 isalso shown, wherein expander 370 has a bore 3702 adapted to accept screw70 therein. Note that the distal end alone of each of screw 170 andexpander 370 is shown. However, it is contemplated that a placementinstrument 130 (not shown in FIG. 39 ) is configured to couple withspacer 350. Unlike the device of FIGS. 7-10 , screw 170 would bepositioned inside expander 370, and the latter would be in turnpositioned within screw 160.

FIG. 40A illustrates that rotation of expander 370 relative to spacer350 will drive segment 3502 away from segment 3504 and increase thelength L of implant 350. FIG. 40B shows the expanded implant 350 afterremoval of screw 170 and expander 370.

The expanded spacer may be left as shown in FIG. 40B or an additionalsegment 380 may be attached to spacer 350 within the cavity 3509 createdby the separation of segments 3502 and 3504. The addition of segment 380provides more bone contact/abutment surface than expanded spacer 350alone, since top and bottom surfaces 3802 of segment 380 will at leastpartially fill cavity 3509. FIG. 41B illustrates segment 380, whereasFIG. 41A shows one segment 380 coupled to expanded spacer 350 and asecond segment 380 positioned to be advanced into cavity 3509. Teeth3808 are used to lock segment 380 onto extension 35045 on segment 3504.

While each of the segment 380 can be separate members that are added toexpanded spacer 350 (as shown), they may alternative be wedge-shapedsegments that are implanted as a sub-segment of implant 350, whereinadvancement of the wedge-shaped segment between segments 3502 and 3504is performed after positioning of spacer 350 into the disc space, andwherein the advanced segment 380 both creates a cavity 3509 and fills itin (this embodiment is not shown).

In use, the implantable spacer 350 is configured to be passed though thepsoas muscle while in a first configuration and then to expand withinthe disc space to a second configuration, wherein the length of spacer350 is greater in the second configuration than in the firstconfiguration. (The length of the device refers to long axis of thespacer, which, in use, is substantially positioned in the direction of asagittal plane through the implanted disc space and measured in theanterior to posterior direction.)

FIG. 42 schematically illustrates the exemplary procedure, whereininstrument 130 attaches implantable spacer 350 prior to expansion (asshown in FIG. 37A) and then guides said spacer 350 through Corridor K ofthe psoas muscle. After spacer 350 is positioned within the target discspace, it is transitioned into the second configuration (as shown inFIG. 37B), wherein the second configuration is of greater length thanthe first spacer configuration. While spacer 350 is shown in both theexpanded and non-expanded state in FIG. 42 , it is to be understood thatthree different steps of the procedure are illustrated and not twoseparate spacers 350. That is, step 1 shows spacers 140 and 350 attachedinstrument 130 and positioned within the body cavity of the individualbut outside of the spine and the psoas muscle. In step 2, spacers 140and 350 traverse the psoas muscle thought corridor K (instrument notshown while in the muscle). In step 3, spacers 140 and 350 have beenpositioned at opposing side of implanted disc space (and sitting on theepiphyseal ring) and transitioned into the expanded state—withsubsequent complete removal of instrument 130. Note that the length ofspacer 350 (as measured in the anterior to posterior plane of the discspace) in the second configuration is greater than the width W ofcorridor K, through which spacer 350 traversed the psoas muscle whilebeing implanted into the disc space.

Note that spacer 140 is also shows as having been expanded to a greaterlength after being positioned within the disc space. While notseparately illustrated, it is understood that spacer 140 can be made toexpand in a manner similar to that illustrated for spacer 350. It isrecognized, however, that many other mechanisms can be used to produceimplantable spacers of expandable length. In one embodiment, the widthof the expandable spacer (as measured in the coronal plane of the spine)may be less or equal to the width of the non-expanded spacer. In anotherembodiment, the width my greater in the expanded state than in thenon-expanded state. That is, the width may change with transition fromthe first to the second configuration or it may remain constant.

In the herein-described exemplary embodiment of the method of deviceuse, at least two implantable spacers are coupled to an implantationinstrument (such as, for example, instrument 130) wherein at least oneof the implantable spacers is configured to have an expandable length.The spacer width may be changeable or it may remain constant. Thespacers are not directly attached to one another but are at leastpartially separated by a cavity configured to house bone graft material.The bone graft material is positioned outside at least one of saidimplantable implants but within a cavity of the implantation instrument.A direct lateral corridor (such as corridor 105; FIG. 4 ) to the targetdisc space is used to implant the spacers. (Note that trajectories otherthan a direct lateral approach may be alternatively used.) In the lumbarspine, the psoas muscle must be traversed in order to position thespacers in the target disc space. After placement of the spacers in thedisc space, the at least one expandable spacer is increased in lengthand the placement instrument is removed from the disc space. In thisway, a spacer is positioned on opposing lateral ends of the disc spacewith the bone graft material positioned there between. At least one ofthe implanted spacers has a length greater than the trans-psoas corridorused to deliver said spacer to the target disc space in one embodiment.At least one of the implanted spacers does not contain an internalcavity that also contains or is configured to contain bone graftmaterial.

The disclosed devices or any of their components can be made for exampleof any biologically adaptable or compatible materials. Materialsconsidered acceptable for biological implantation are well known andinclude, but are not limited to, stainless steel, titanium, tantalum,combination metallic alloys, various plastics, resins, ceramics,biologically absorbable materials and the like. Any components may bealso coated/made with nanotube materials to further impart uniquemechanical or biological properties. In addition, any components may bealso coated/made with osteo-conductive (such as deminerized bone matrix,hydroxyapatite, and the like) and/or osteo-inductive (such asTransforming Growth Factor “TGF-B,” Platelet-Derived Growth Factor“PDGF,” Bone-Morphogenic Protein “BMP,” and the like) bio-activematerials that promote bone formation. Further, any surface may be madewith a porous ingrowth surface (such as titanium wire mesh,plasma-sprayed titanium, tantalum, porous CoCr, and the like), providedwith a bioactive coating, made using tantalum, and/or helical rosettecarbon nanotubes (or other carbon nanotube-based coating) in order topromote bone in-growth or establish a mineralized connection between thebone and the implant, and reduce the likelihood of implant loosening.The system or any of its components can also be entirely or partiallymade of a shape memory material or other deformable material. Lastly,any of the implanted spaces that are disclosed may be partially orcompletely made out of bone and/or bone graft material.

It will be recognized that while certain aspects of the disclosure aredescribed in terms of a specific sequence of steps of a method, thesedescriptions are only illustrative of the broader methods thereof, andmay be modified as required by the particular application. Certain stepsmay be rendered unnecessary or optional under certain circumstances.Additionally, certain steps or functionality may be added to thedisclosed embodiments, or the order of performance of two or more stepspermuted. All such variations are considered to be encompassed withinthe present disclosure and claimed herein.

While the above detailed description has shown, described, and pointedout novel features of the disclosure as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the disclosure. Theforegoing description is of the best mode presently contemplated. Thisdescription is in no way meant to be limiting, but rather should betaken as illustrative of the general principles. The scope of thepresent disclosure should be determined with reference to the claims.

1.-12. (canceled)
 13. A device assembly configured for use in treatmentof a spinal segment, the spinal segment comprising a superior vertebralbone, an inferior vertebral bone and an intervertebral disc spacepositioned therebetween, the device assembly comprising: a firstimplantable member, the first implantable member comprising a superiorsurface configured to abut the superior vertebral bone and an inferiorsurface configured to abut the inferior vertebral bone; a secondimplantable member, the second implantable member separately formed fromthe first implantable member, the second implantable member comprising:a first extension comprising a first aperture, the first apertureconfigured to receive a first fastener, the first fastener configured tobe at least partially advanced through the first aperture and into afirst of the superior vertebral bone or the inferior vertebral bone; anda second aperture; and a placement instrument configured to deliver thefirst implantable member and the second implantable member to the spinalsegment.
 14. The device assembly of claim 13, wherein the placementinstrument comprises: a proximal segment comprising a handle extendedalong a longitudinal axis; a distal segment configured to engage thefirst implantable member; an intermediate segment disposed between theproximal segment and the distal segment, the intermediate segmentcomprising an intermediate coupler configured to engage the secondimplantable member; and a retention apparatus configured to: (i) extendthrough the second aperture of the second implantable member, and (ii)engage with the first implantable member, the retention apparatuscomprising a member having a distal end, the member further having alength greater than a width thereof, the member configured to align withthe longitudinal axis.
 15. The device assembly of claim 13, wherein saidfirst implantable member further comprises a cavity configured toreceive at least one bone forming material.
 16. The device assembly ofclaim 14, wherein the first implantable member further comprises aproximal side surface and an opposing distal side surface, the proximalside surface connecting the superior surface and the inferior surfaceand configured to: (i) engage with the distal end of the retentionapparatus, and (ii) after the engagement with the distal end of themember of the retention apparatus, be positioned to face the secondimplantable member.
 17. The device assembly of claim 14, wherein: thesecond implantable member further comprises a second extension, thesecond extension comprising a third aperture that is configured toreceive a second fastener, the second fastener configured to be at leastpartially advanced through the third aperture and into a second of thesuperior vertebral bone or the inferior vertebral bone; and the secondaperture of the second implantable member is positioned between thefirst extension and the second extension.
 18. The device assembly ofclaim 14, further configured such that when the first implantable memberis engaged with the distal segment of the placement instrument, and thesecond implantable member is engaged with the intermediate coupler ofthe intermediate segment, a cavity is formed between the firstimplantable member and the second implantable member, the cavityconfigured to receive at least a bone forming material.
 19. The deviceassembly of claim 14, wherein the proximal segment of the placementinstrument further comprises a channel aligned with the longitudinalaxis, the retention apparatus configured to be inserted through thechannel in order to enable the engagement of the retention apparatuswith the first implantable member.
 20. A delivery device and implantassembly comprising: a first implantable member, the first implantablemember comprising a superior surface configured to abut a superiorvertebral bone of a spinal segment and an inferior surface configured toabut an inferior vertebral bone of the spinal segment; a secondimplantable member, the second implantable member separable from thefirst implantable member and comprising at least a first extension, thefirst extension comprising a first aperture configured to receive afirst fastener, the first fastener sized to be at least partiallyadvanced through the first aperture and into one of the superiorvertebral bone or the inferior vertebral bone; and a placementinstrument configured to deliver the first implantable member and thesecond implantable member to the spinal segment, the placementinstrument comprising: a proximal segment comprising a handle, thehandle having a longitudinal axis and being greater in length thanwidth, the length measured along the longitudinal axis; a first prongcomprising: a distal segment comprising a first surface configured toengage the first implantable member; an intermediate segment disposedbetween the proximal segment and the distal segment and comprising asecond surface configured to engage with the second implantable member;and a retention apparatus comprising an elongate member, the elongatemember configured to (i) be aligned with the longitudinal axis of thehandle, and (ii) engage the first implantable member; wherein theplacement instrument is extended from a proximal end of the proximalsegment to a distal end of the distal segment; and wherein the firstsurface of the distal segment is positioned a greater distance from theproximal end than the second surface of the intermediate segment, asmeasured along the longitudinal axis.
 21. The delivery device andimplant assembly of claim 20, wherein the first implantable memberfurther comprises a proximal side surface and an opposing distal sidesurface, the proximal side surface connecting the superior surface andthe inferior surface of the first implantable member and configured toengage with a distal portion of the retention apparatus so as to beoriented toward the second implantable member.
 22. The delivery deviceand implant assembly of claim 21, wherein the proximal side surface isfurther configured to receive the distal portion of the retentionapparatus.
 23. The delivery device and implant of claim 21, wherein thesecond implantable member further comprises a distal side surface, anopposing proximal side surface, the distal side surface of the secondimplantable member configured to, after the engagement of the secondsurface of the intermediate segment of the first prong with the secondimplantable member, face the proximal side surface of the firstimplantable member.
 24. The delivery device and implant of claim 20,wherein the first implantable member further comprises a first sidesurface and an opposing second side surface, the first side surfaceconnecting the superior surface and the inferior surface of the firstimplantable member, and configured to engage with the first surface ofthe distal segment.
 25. The delivery device and implant of claim 20,wherein the second implantable member further comprises a secondextension, the second extension comprising a second aperture that isconfigured to receive a second fastener, the second fastener sized to beat least partially advanced through the second aperture and into one ofthe superior vertebral bone or the inferior vertebral bone into whichthe first fastener is not advanced.
 26. The delivery device and implantof claim 20, wherein a third aperture of the second implantable memberis positioned between the first extension and the second extension. 27.The delivery device and implant of claim 20, wherein the proximalsegment further comprises a channel aligned with the longitudinal axis,the retention apparatus configured to be inserted through the channel inorder to enable the engagement of the retention apparatus with the firstimplantable member.
 28. A device assembly configured to deliver a firstimplantable member and a second implantable member to a spinal segment,the spinal segment comprising a superior vertebral bone, an inferiorvertebral bone and an intervertebral disc space disposed therebetween,the first implantable member comprising a superior surface configured toabut the superior vertebral bone and an inferior surface configured toabut the inferior vertebral bone, the second implantable memberseparately formed from the first implantable member and comprising afirst side surface, a second opposing side surface, and at least oneextension, the at least one extension comprising a first apertureconfigured to receive a fastener, the fastener sized to be at leastpartially advanced through the first aperture and into one of thesuperior vertebral bone and the inferior vertebral bone, the deviceassembly comprising: a placement instrument configured to deliver thefirst implantable member and the second implantable member to the spinalsegment, the placement instrument comprising: a proximal segmentcomprising an elongate body extended along a longitudinal axis of theproximal segment, the elongate body comprising a channel aligned withthe longitudinal axis; a distal segment; and an intermediate segmentpositioned at least partially between the proximal segment and thedistal segment and comprising at least a first portion of a firstextension element, the first portion of the first extension elementconfigured to engage the first side surface of the second implantablemember; and a retention apparatus configured for use with the placementinstrument, the retention apparatus comprising: an elongate memberconfigured to be aligned with the longitudinal axis of the proximalsegment, and for insertion through the channel; and a distal coupler,the distal coupler configured to threadedly engage the first implantablemember.
 29. The device assembly of claim 28, wherein the distal segmentis configured to engage the first implantable member.
 30. The deviceassembly of claim 29, wherein the distal segment comprises a secondportion of the first extension element.
 31. The device assembly of claim28, wherein: the first implantable member further comprises a proximalside surface and an opposing distal side surface, the proximal sidesurface connecting the superior surface and the inferior surface andconfigured to engage with a distal end of the retention apparatus so asto oriented toward the second implantable member; and the distal end ofthe retention apparatus is configured to be received in the proximalside surface of the first implantable member.
 32. The device assembly ofclaim 28, wherein the intermediate segment further comprises a firstportion of a second extension element, the first portion of the secondextension element configured to engage the second side surface of thesecond implantable member, the second side surface of the secondimplantable member opposing the first side surface.